Initial position detection of the motor

Abstract

A method for detecting an initial position of an electric motor includes determining a delta voltage for each of three pairs of stator windings by sequentially energizing and de-energizing each pair. The delta voltage is measured via an unenergized stator winding connected to the center tap of each corresponding pair. A minimum delta voltage is determined based on the absolute value of the minimum of the three delta voltages. The minimum delta voltage is associated with a remaining stator winding not included in the corresponding pair. Two delta voltages not associated with the minimum delta voltage are compared to determine the proximity of the remaining stator winding to one of the D-axis and the Q-axis of the rotor of the electric motor.

Description

Technical Field

[0001] The present disclosure relates generally to electric motors, and more particularly, to determining rotor position and polarity prior to starting an electric motor. Background Art

[0002] Permanent magnet synchronous motors (PMSMs) typically undergo a rotor alignment process before startup. Without rotor alignment, the PMSM may temporarily reverse direction or experience mechanical vibration during startup, which is unacceptable in many actuator or electric vehicle applications. Traditionally, sensors including Hall devices, optical encoders, and inductive encoders have been used to detect rotor position. Using sensors to detect rotor position increases system complexity and reduces safety due to the potential for additional component failures.

[0003] Recent sensorless systems for detecting rotor position rely on time-consuming current measurements, precise sampling of the stator inductor voltage, and / or sampling of the time-varying bus voltage. Each of these approaches reduces the reliability of rotor position detection, increases cost, complexity, and, in some cases, increases motor startup time. Furthermore, conventional techniques for determining rotor position result in low accuracy in the estimated rotor position. Summary of the Invention

[0004] According to a first aspect, there is provided a method for detecting an initial position of a motor, comprising:

[0005] for each of a respective pair of stator windings selected from two of the three stator windings, wherein each of the three stator windings is connected to a neutral node, determining a respective stator delta voltage, each respective stator delta voltage being one of a plurality of delta voltages determined by: applying a first voltage pulse across the respective pair while measuring a respective first voltage at the neutral node, applying a discharge path across the respective pair while measuring a respective second voltage at the neutral node, and determining the delta voltage by subtracting the respective first voltage from the respective second voltage;

[0006] determining a minimum delta voltage based on a minimum of the absolute values of each of the three respective stator delta voltages, the minimum delta voltage being associated with a remaining stator winding of the three stator windings that is not included in the respective pair;

[0007] determining a proximity of the remaining stator winding corresponding to the minimum delta voltage to one of a D-axis of a rotor of the electric motor and a Q-axis of the rotor by comparing the stator delta voltages of the two stator windings not associated with the minimum delta voltage; and

[0008] The rotor polarity of the rotor is determined by comparing a first rotor delta connection voltage with a second rotor delta connection voltage, wherein the first rotor delta connection voltage and the second rotor delta connection voltage are each one of the plurality of delta connection voltages determined based on a pair of stator windings including the remaining stator winding associated with the minimum delta connection voltage.

[0009] According to one or more embodiments, the first voltage and the second voltage of the neutral node are measured at ends of the remaining stator windings connected to the neutral node, wherein the remaining stator windings are not powered.

[0010] According to one or more embodiments, the first and second voltage pulses for determining the rotor polarity have a long duration capable of magnetically saturating the remaining stator winding associated with the minimum delta voltage.

[0011] According to one or more embodiments, the first and second voltage pulses for determining the polarity of the rotor have a short duration capable of preventing the rotor from physically rotating.

[0012] According to one or more embodiments, the minimum absolute voltage corresponds to the U phase, the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the V phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the V phase is less than or equal to the corresponding stator voltage of the W phase.

[0013] According to one or more embodiments, the initial position of the rotor is:

[0014] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 0 degrees relative to a reference angle,

[0015] When the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 180 degrees relative to the reference angle,

[0016] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally -90 degrees relative to the reference angle, and

[0017] When the first absolute value of the first rotor delta voltage is less than or equal to the second absolute value of the second rotor delta voltage and the remaining stator windings are close to the Q-axis, nominally 90 degrees relative to the reference angle.

[0018] According to one or more embodiments, the minimum absolute voltage corresponds to the V phase, the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the U phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the U phase is less than or equal to the corresponding stator voltage of the W phase.

[0019] According to one or more embodiments, the initial position of the rotor is:

[0020] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 30 degrees relative to the reference angle,

[0021] When the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D-axis, nominally -150 degrees relative to the reference angle,

[0022] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, nominally 120 degrees relative to the reference angle, and

[0023] When the first absolute value of the first rotor delta voltage is less than or equal to the second absolute value of the second rotor delta voltage and the remaining stator windings are close to the Q-axis, nominally -60 degrees relative to the reference angle.

[0024] According to one or more embodiments, the minimum absolute voltage corresponds to the W phase, the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the U phase is greater than the corresponding stator voltage of the V phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the U phase is less than or equal to the corresponding stator voltage of the V phase.

[0025] According to one or more embodiments, the initial position of the rotor is:

[0026] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally -120 degrees relative to the reference angle,

[0027] When the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 60 degrees relative to the reference angle,

[0028] When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, nominally 150 degrees relative to the reference angle, and

[0029] When the first absolute value of the first rotor delta voltage is less than or equal to the second absolute value of the second rotor delta voltage and the remaining stator windings are close to the Q-axis, nominally -30 degrees relative to the reference angle.

[0030] According to a second aspect of the present invention, there is provided a device comprising:

[0031] a rotor of an electric motor, the rotor comprising a direct (D) axis and a quadrature (Q) axis, wherein the D axis defines a first path of maximum reluctance of the rotor and the Q axis defines a second path of maximum torque production; and

[0032] a plurality of stator windings of the electric motor, wherein three pairs of stator windings are selected from the plurality of stator windings; and

[0033] A controller configured to:

[0034] determining a delta voltage for each pair of stator windings by sequentially energizing and de-energizing each pair of stator windings, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair,

[0035] determining a minimum delta voltage based on a minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with the remaining stator winding not included in the corresponding pair, and

[0036] The two delta voltages not associated with the minimum delta voltage are compared to determine a proximity of the remaining stator winding to one of the D-axis of the rotor and the Q-axis of the rotor.

[0037] According to one or more embodiments, the electric motor comprises a permanent magnet synchronous motor (PMSM).

[0038] According to one or more embodiments, the electric motor comprises a brushless direct current (BLDC) motor.

[0039] According to one or more embodiments, the controller is further configured to sequentially energize and de-energize a pair of stator windings including the remaining stator winding associated with the minimum delta connection voltage to measure a first rotor delta connection voltage and a second rotor delta connection voltage, wherein the first rotor delta connection voltage is measured by applying a first voltage pulse in an opposite direction to a second voltage pulse used to measure the second rotor delta connection voltage; and the rotor polarity of the rotor is determined by comparing the first rotor delta connection voltage to the second rotor delta connection voltage.

[0040] According to one or more embodiments, the controller is further configured to energize each pair of stator windings by sequentially connecting each pair of stator windings to one of a power source and ground via respective shorting diode connections.

[0041] According to a third aspect of the present invention, there is provided a method for detecting an initial position of a motor, comprising:

[0042] determining a delta voltage for each of three pairs of stator windings by sequentially energizing and de-energizing each pair, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair;

[0043] determining a minimum delta voltage based on a minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with the remaining stator winding not included in the corresponding pair; and

[0044] The two delta-connected voltages, which are not associated with the minimum delta-connected voltage, are compared to determine the proximity of the remaining stator winding to one of a direct (D) axis of the rotor of the electric motor and a quadrature (Q) axis of the rotor, wherein the D axis defines a first path of maximum reluctance of the rotor and the Q axis defines a second path of maximum torque production.

[0045] According to one or more embodiments, further comprising sequentially energizing and de-energizing a pair of stator windings including the remaining stator winding associated with the minimum delta connection voltage to measure a first rotor delta connection voltage and a second rotor delta connection voltage, wherein the first rotor delta connection voltage is measured by applying a first voltage pulse in an opposite direction to a second voltage pulse used to measure the second rotor delta connection voltage, and the rotor polarity of the rotor is determined by comparing the first rotor delta connection voltage to the second rotor delta connection voltage.

[0046] According to one or more embodiments, the first and second voltage pulses for determining the rotor polarity have a long duration capable of magnetically saturating the remaining stator winding associated with the minimum delta voltage.

[0047] According to one or more embodiments, the first and second voltage pulses for determining the polarity of the rotor have a short duration capable of preventing the rotor from physically rotating.

[0048] According to one or more embodiments, energizing each of the three pairs of stator windings includes connecting each respective pair to one of a power source and ground through a respective shorting diode connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention is illustrated by way of example and is not limited by the accompanying drawings, in which like reference numerals indicate similar elements. Elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

[0050] Figure 1 、 Figure 2 and Figure 3 is a schematic diagram illustrating example embodiments of various physical relationships between stator self-inductance and rotor permanent magnet positions for initial determination of rotor position.

[0051] Figure 4 and Figure 5 is a schematic diagram of a motor configured during a pulse injection interval and a freewheeling interval, respectively, according to an example embodiment of the present disclosure.

[0052] Figure 6 and Figure 7 is a schematic diagram illustrating example embodiments of two physical relationships between stator self-inductance and rotor permanent magnet positions for determination of rotor polarity.

[0053] Figure 8 is a polar plot illustrating a determined rotor position according to an example embodiment of the present disclosure.

[0054] Figure 9 is a method for determining Figure 8 Flowchart representation of the rotor position method.

[0055] Figure 10 This is a further illustration of an exemplary embodiment according to the present disclosure. Figure 8 and Figure 9 Tabular view of the determination of the rotor position.

[0056] Figure 11 is a flowchart representation of a method for initial position detection of a motor according to an example embodiment of the present disclosure.

[0057] Figure 12 is a flowchart representation of a method for initial position detection of a motor according to an example embodiment of the present disclosure. DETAILED DESCRIPTION

[0058] Embodiments described herein provide detection of the position and polarity of the rotor to facilitate starting of the motor. Three short pulses are injected sequentially into each pair of three stator windings, with measurements taken during the pulse injection interval and the 'freewheeling' interval. The freewheeling interval occurs when the injected voltage pulses are removed and the stator generates a back electromotive force (EMF) as the stator inductor is de-energized. A relative voltage measurement is performed on each pair of stator windings by subtracting the freewheeling voltage from the injected voltage during the pulse injection period. In one embodiment, the voltage difference of each pair of inductors is measured by a floating phase (e.g., the remaining inductor that does not form an inductor pair) to determine the center tap voltage. The value of the center tap voltage is related to the ability of the stator inductor to generate and release magnetic field energy, which is in turn related to the stator inductance. The stator inductance changes with the position of the stator inductor relative to the rotor and can therefore be used to determine a pair of completely opposite rotor positions.

[0059] The rotor polarity is further determined by applying two long voltage pulses across the stator pair, including the stator windings closest to the rotor, and comparing measurements taken during the injection interval and the freewheeling interval. Each voltage pulse is applied to the stator pair with opposite polarity. The long pulses are designed to magnetically saturate the rotor core without causing physical rotation of the rotor. By exploiting the nonlinear magnetic saturation phenomenon of the rotor core, the two measured voltages for each applied pulse will increase or decrease depending on the rotor polarity. Therefore, among other advantages, rotor position and polarity are determined with minimal applied energy, reduced noise, and improved reliability, robustness, and accuracy. Specifically, relative voltage measurements are taken at the center tap of each inductor to reduce errors due to bus voltage variations, enhance data resolution, and improve reliability. Voltage measurement time is shorter than the time required to perform current measurements used in previous solutions. The resulting extremely fast execution time for calculating rotor position is crucial for automotive applications. Due to the reduced energy injected into the inductor, the noise generated during motor startup is also very low.

[0060] Figure 1 、 Figure 2 and Figure 3 An example embodiment of the physical relationship between stator self-inductance and rotor position is shown. For simplicity, the mutual inductance of the stator windings does not need to be analyzed because the induced voltage caused by the mutual inductance does not change significantly. Due to the magnetic convexity, the magnitude of each stator inductance is related to the magnetic resistance formed by the stator and rotor in the magnetic circuit. A larger magnetic reluctance (e.g., reluctance) reduces the inductance value. Similarly, a smaller magnetic reluctance of the stator winding increases the self-inductance of the stator winding. The magnetic reluctance represents the opposite of the magnetic flux. Therefore, when the rotor is aligned with the stator winding, the magnetic flux flows more easily, resulting in an increase in the magnetic reluctance and therefore a decrease in the self-inductance.

[0061] Figure 1 An embodiment of a three-phase motor 10 is shown including a U-phase end 12 of a U-phase stator winding 13, a V-phase end 14 of a V-phase stator winding 15, and a W-phase end 16 of a W-phase stator winding 17. A neutral node 18 (or "center tap") connects each of the three stator windings. A rotor 19 includes a north pole 20 and a south pole 22. A direct (D) axis 24 defines the path of maximum magnetic resistance of the rotor. A positive (Q) axis 26 defines the path of maximum torque production. Figure 1 In the example, the inductance (Lu) of the U-phase stator winding 13 is smaller than the inductance (Lv) of the V-phase stator winding 15. The inductance Lv is equal to the inductance (Lw) of the W-phase stator winding 17. Figure 1 Example embodiment 10 with Figure 2 Example embodiment 30 and Figure 3 For comparison with the example embodiment 50, Figure 2 The Lu inductance is greater than Figure 3 Lu inductor, Figure 3 The Lu inductance is greater than Figure 1 To reiterate, due to different rotor positions, the Lu inductance of the U-phase stator winding 13 is Figure 1 The smallest in Figure 2 The largest.

[0062] Figure 4 and Figure 5 Example embodiments 70 and 110 of a motor are shown for a pulse injection interval and a freewheeling interval, respectively. Figure 4 In example embodiment 70, the positive terminal of voltage source 71 is connected to U-phase terminal 12 via diode 72, which can be short-circuited by switch 74. The negative terminal of voltage source 71 is connected to U-phase terminal 12 via diode 76, which can be short-circuited by switch 78. The positive terminal of voltage source 71 is connected to V-phase terminal 14 via diode 82, which can be short-circuited by switch 84. The negative terminal of voltage source 71 is connected to V-phase terminal 14 via diode 86, which can be short-circuited by switch 88. The positive terminal of voltage source 71 is connected to W-phase terminal 16 via diode 92, which can be short-circuited by switch 94. The negative terminal of voltage source 71 is connected to W-phase terminal 16 via diode 96, which can be short-circuited by switch 98. Each of example embodiments 70 and 110 includes a controller 100. In one example embodiment, controller 100 includes a combination of one or more of a state machine, machine code, and / or firmware configured to control switches 74, 78, 94, 98, 84, and 88.

[0063] In the exemplary embodiment 70, a pair of stator windings includes a U-phase stator winding 13 and a W-phase stator winding 17. During the pulse injection interval, the controller 100 short-circuits diode 72 using switch 74 and diode 96 using switch 98. Consequently, current 102 flows from the positive terminal of voltage source (Vdc) 71 through switch 74 and through the U-phase stator winding 13. Current 104 flows through the W-phase stator winding 17 and switch 98 to the negative terminal of voltage source 71. Thus, the pair of stator windings formed by the U-phase stator winding 13 and the W-phase stator winding 17 is energized. With the U-phase terminal 12 connected to the positive terminal of voltage source 71 and the W-phase terminal 16 connected to the negative terminal of voltage source 71, the voltage applied to the pair of stator windings (e.g., the "motor stator") is Uuw. The voltage measured at the V-phase terminal 14 through the floating V-phase stator winding 14 is substantially the same as the voltage at the neutral node 18. The voltage Vv1 of the neutral node 18 after the pulse injection interval is obtained by the following formula, where Lw and Lu are the inductances of the W-phase stator winding 17 and the U-phase stator winding 13, respectively:

[0064] (1) Vv1=[Lw / (Lu+Lw)]*Vdc

[0065] In the exemplary embodiment 110, a pair of stator windings includes a U-phase stator winding 13 and a W-phase stator winding 17. During the freewheeling interval, the controller 100 opens the switches 74 and 98. As a result, a current 106 flows from the negative terminal of the voltage source 71 through the diode 76 and through the U-phase stator winding 13. A current 108 flows through the W-phase stator winding 17 and the diode 92 to the positive terminal of the voltage source 71. Thus, the pair of stator windings formed by the U-phase stator winding 13 and the W-phase stator winding 17 is de-energized, thereby generating a back EMF to generate the currents 106 and 108. The voltage Vv2 of the neutral node 18 after this pulse injection interval is obtained by the following equation:

[0066] (2) Vv2=[Lu / (Lu+Lw)]*Vdc

[0067] Therefore, the delta voltage across a pair of stator windings is given by:

[0068] (3) ΔVv=Vv2-Vv1

[0069] The process of energizing and deenergizing each of the multiple stator winding pairs for determining ΔVv, as described for the stator pair formed by the U-phase stator winding 13 and the W-phase stator winding 17, is repeated with the remaining stator pairs to generate ΔVu and ΔVw. Specifically, ΔVu is generated based on measurements of the pulse injection interval and freewheeling interval of the voltage pulse Uvw across the V-phase stator winding 15 and the W-phase stator winding 17. ΔVw is generated based on measurements of the pulse injection interval and freewheeling interval of the voltage pulse Uuv across the U-phase stator winding 13 and the V-phase stator winding 15.

[0070] Next, the minimum delta voltage is determined based on the minimum of the absolute values of each of the corresponding stator delta voltages ΔVu, ΔVv, and ΔVw, as given by:

[0071] (3) ΔVmin = min(|ΔVu|, |ΔVv|, |ΔVw|)

[0072] like Figure 1 and Figure 2 As shown in , when ΔVmin=|ΔVu|, the U-phase stator winding 13 is aligned closest to the D-axis 24 or the Q-axis 26 compared to the remaining two stator windings 15 and 17. Conversely, if ΔVmin=|ΔVv|, the V-phase stator winding 15 is aligned closest to the D-axis 24 or the Q-axis 26, and if ΔVmin=|ΔVw|, the W-phase stator winding 17 is aligned closest to the D-axis 24 or the Q-axis 26.

[0073] Two of the previously determined delta connection voltages determined based on each pair of stator windings including the stator winding associated with ΔVmin are used to distinguish whether the stator winding associated with ΔVmin is closest to the D-axis 24 or closest to the Q-axis 26. For example, when ΔVmin=|ΔVu|, ΔVv (determined based on Uuw) and ΔVw (determined based on Uuv) are used to analyze whether the U-phase stator winding 13 is close to the D-axis 24 or close to the Q-axis 26. Specifically, when ΔVv is greater than ΔVw, the U-phase stator winding 13 is close to the D-axis 24. When ΔVv is less than or equal to ΔVw, the U-phase stator winding 13 is close to the Q-axis 26. In another embodiment, a single-ended measurement is used, in which if ΔVw is greater than zero, the U-phase stator winding 13 is close to the Q-axis 26, otherwise the U-phase stator winding 13 is close to the D-axis 24.

[0074] Once the proximity of the stator windings (associated with ΔVmin) to the shaft is determined, the polarity of the rotor 19 aligned with the stator windings can be determined. Figure 6 The example embodiment 120 shows the north pole 20 of the rotor 19 aligned with the U-phase stator winding 13. In contrast, Figure 7The example embodiment 130 shows the south pole 22 of the rotor 19 aligned with the U-phase stator winding 13. A voltage pulse signal is applied to a pair of stator windings including a stator winding associated with ΔVmin to determine the polarity of the rotor 19. For example, referring to Figure 6 and Figure 7 , a voltage pulse is applied to a pair of stators including the U-phase stator winding 13 and the V-phase stator winding 15 , or to the U-phase stator winding 13 and the W-phase stator winding 17 .

[0075] In one example, a long voltage pulse Uuv is applied to a pair of stator windings including a U-phase stator winding 13 and a V-phase stator winding 15, using the nonlinear magnetic saturation characteristics of the stator core to determine the rotor polarity. The applied long voltage pulse is long enough to ensure that the stator windings (e.g., Figure 6 The U-phase stator winding 13 in the embodiment is magnetically saturated and short enough to prevent the rotor 19 from physically rotating. Figure 6 As shown in , when a long Uuv is applied across terminals 12 and 14, the current in the U-phase stator winding 13 will weaken the effect of the rotor flux on Lu and Lv, thereby reducing the values of Lu and Lv. However, compared to the V-phase stator winding 15, the U-phase stator winding 13 is more likely to be magnetically saturated, so the equation dLu / di>dLv / di holds. To reiterate, the inductance Lu of the U-phase stator winding 13 will be significantly reduced compared to Lv. Conversely, if Figure 7 As shown in , the inductance Lu will increase more significantly than Lv.

[0076] First, a long voltage pulse Uuv is applied to a pair of stators in the pulse injection interval to determine Vw1, then the long voltage pulse Uuv is applied to the freewheeling interval to determine Vw2, and then the difference between Vw2-Vw1 is determined to determine ΔVw1. Figure 4 and Figure 5 The voltage sensing is then reversed to apply a long voltage pulse Uvu, and ΔVw2 is determined in a similar manner to ΔVw1. Finally, if |ΔVw1|>|ΔVw2|, the north pole 20 is aligned with the U-phase stator winding 13, as shown in FIG. Figure 6 Otherwise, the south pole 22 is aligned with the U-phase stator winding 13, as shown in FIG. Figure 7 As shown in .

[0077] Figure 8 is a polar coordinate diagram showing various positions of the rotor 19 according to an example embodiment of the present disclosure. Figure 8 , the position of the rotor 19 is resolved to within plus or minus 15 degrees, wherein the angular ranges 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, and 170 are resolved relative to a reference angle at 0 degrees. Figure 6 、 Figure 7 and Figure 8 In one example embodiment, ΔVmin=|ΔVu|. Thus, the rotor 19 is aligned with the U-phase stator winding 13 at an angular range of 140, 170, 154, 156, 148, 146, 162, or 164. After determining that the U-phase stator winding 13 is close to the D-axis 24, the rotor 19 is resolved to be aligned with 140, 170, 154, or 156. After resolving the polarity direction of the rotor 19, the rotor alignment will be Figure 6 In the case of , it corresponds to an angular range of 140 or 170, or Figure 7 The case corresponds to 154 or 156.

[0078] Figure 9 is a method for determining Figure 8 The method 180 starts at 182. At 184, according to Figure 4 and Figure 5 A first set of voltage pulses is injected across each pair of stator windings. At 186, the values of ΔVu, ΔVv, and ΔVw are calculated. At 190, 192, and 194, one of three decision branches is followed, depending on whether ΔVmin = min(|ΔVu|), min(|ΔVv|), or min(|ΔVw|), respectively.

[0079] At 190, if ΔVmin=min(|ΔVu|), then a second set of long voltage pulses is injected at 200. Figure 6 and Figure 7 The long voltage pulse is further described. At 202, the values of ΔW1 and ΔW2 are determined. At 204, if ΔV>ΔW, the stator winding associated with ΔVmin is close to the D axis 24, otherwise the winding is close to the Q axis 26. At 206, if |ΔW1|>|ΔW2|, the rotor position is 0 degrees at 212 (see Figure 8 140 or 170), otherwise the rotor position is 180 degrees at 210 (see Figure 8 154 or 156). At 208, if |ΔW1|>|ΔW2|, then the rotor position at 216 is -90 degrees (see Figure 8 162 or 164), otherwise the rotor position is 90 degrees at 214 (see Figure 8 146 or 148).

[0080] At 192, if ΔVmin=min(|ΔVv|), then a second set of long voltage pulses is injected at 220. Figure 6 and Figure 7The long voltage pulse is further described. At 222, the values of ΔU1 and ΔU2 are determined. At 224, if ΔU>ΔW, the stator winding associated with ΔVmin is close to the D axis 24, otherwise the winding is close to the Q axis 26. At 226, if |ΔU1|>|ΔU2|, the rotor position is 30 degrees at 232 (see Figure 8 142), otherwise the rotor position is -150 degrees at 230 (see Figure 8 158). At 228, if |ΔU1|>|ΔU2|, then the rotor position at 236 is 120 degrees (see Figure 8 150), otherwise the rotor position is -60 degrees at 234 (see Figure 8 166).

[0081] At 194, if ΔVmin=min(|ΔVw|), then a second set of long voltage pulses is injected at 240. Figure 6 and Figure 7 The long voltage pulse is further described. At 242, the values of ΔV1 and ΔV2 are determined. At 244, if ΔU>ΔV, the stator winding associated with ΔVmin is close to the D axis 24, otherwise the winding is close to the Q axis 26. At 246, if |ΔV1|>|ΔV2|, the rotor position at 252 is -120 degrees (see Figure 8 160), otherwise the rotor position is 60 degrees at 250 (see Figure 8 144). At 248, if |ΔV1|>|ΔV2|, then the rotor position at 256 is 150 degrees (see Figure 8 152), otherwise the rotor position is -30 degrees at 254 (see Figure 8 At 218, method 180 ends.

[0082] Figure 10 This is a further illustration of an exemplary embodiment according to the present disclosure. Figure 8 and Figure 9 Tabular view of the determination of the rotor position. Figure 11 An example embodiment 270 of a method for initial position detection of an electric motor is shown. At 272, a corresponding stator delta voltage (ΔVu, ΔVv, or ΔVw) is determined for each pair of stator windings. At 274, a minimum delta voltage (ΔVmin) associated with the remaining stator windings is determined based on each stator delta voltage. At 276, the proximity of the remaining stator windings corresponding to the minimum delta voltage to the D-axis 24 or the Q-axis 26 of the rotor 19 is determined. At 278, the rotor polarity is determined by comparing the first rotor delta voltage to the second rotor delta voltage (e.g., |ΔW1| > |ΔW2|).

[0083] Figure 12 An example embodiment 280 of a method for initial position detection of a motor is shown. At 282, by energizing each pair (see Figure 4 ) and power failure (see Figure 5 ) to determine the corresponding delta voltage for each pair of stator windings. At 284, a minimum delta voltage associated with the remaining stator windings is determined based on each stator delta voltage. At 286, two delta voltages not associated with the minimum delta voltage are compared to determine the proximity of the remaining stator windings to the D-axis 24 or the Q-axis 26 of the rotor 19.

[0084] As will be appreciated, the disclosed embodiments include at least the following. In one embodiment, a method for detecting an initial position of an electric motor includes: determining, for each of a corresponding pair of stator windings selected from two of three stator windings, wherein each of the three stator windings is connected to a neutral node, a corresponding stator delta voltage, each corresponding stator delta voltage being one of a plurality of delta voltages determined by applying a first voltage pulse across the corresponding pair while measuring a corresponding first voltage at the neutral node, applying a discharge path across the corresponding pair while measuring a corresponding second voltage at the neutral node, and determining the delta voltage by subtracting the corresponding first voltage from the corresponding second voltage. A minimum delta voltage is determined based on a minimum of the absolute values of each of the three corresponding stator delta voltages, the minimum delta voltage being associated with a remaining stator winding of the three stator windings not included in the corresponding pair. A proximity of the remaining stator winding corresponding to the minimum delta voltage to one of a D-axis and a Q-axis of a rotor of the electric motor is determined by comparing the stator delta voltages of two stator windings not associated with the minimum delta voltage. The rotor polarity of the rotor is determined by comparing a first rotor delta connection voltage and a second rotor delta connection voltage, wherein the first rotor delta connection voltage and the second rotor delta connection voltage are each one of a plurality of delta connection voltages determined based on a pair of stator windings including a remaining stator winding associated with a minimum delta connection voltage.

[0085] Alternative embodiments of the method for initial position detection of an electric motor include one of the following features or any combination of the following features. A first voltage and a second voltage at a neutral node are measured at ends of the remaining stator winding connected to the neutral node, wherein the remaining stator winding is not energized. The first voltage pulse and the second voltage pulse for determining the polarity of the rotor have a long duration capable of magnetically saturating the remaining stator winding associated with the minimum delta connection voltage. The first voltage pulse and the second voltage pulse for determining the polarity of the rotor have a short duration capable of preventing the rotor from physically rotating. The minimum absolute voltage corresponds to the U phase, the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the V phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the V phase is less than or equal to the corresponding stator voltage of the W phase. The minimum absolute voltage corresponds to the U phase and the initial position of the rotor is: when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally 0 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally 180 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally -90 degrees relative to the reference angle; and when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally 90 degrees relative to the reference angle. The minimum absolute voltage corresponds to the V phase, the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the U phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the U phase is less than or equal to the corresponding stator voltage of the W phase. The minimum absolute voltage corresponds to the V phase and the initial position of the rotor is: when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally 30 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally -150 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally 120 degrees relative to the reference angle; and when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally -60 degrees relative to the reference angle.The minimum absolute voltage corresponds to the W phase, and the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the U phase is greater than the corresponding stator voltage of the V phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the U phase is less than or equal to the corresponding stator voltage of the V phase. The minimum absolute voltage corresponds to the W phase and the initial position of the rotor is: when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally -120 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, it is nominally 60 degrees relative to the reference angle; when the first absolute value of the first rotor delta connection voltage is greater than the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally 150 degrees relative to the reference angle; and when the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally -30 degrees relative to the reference angle.

[0086] In another embodiment, an apparatus includes a rotor for an electric motor, the rotor including a direct (D) axis and a quadrature (Q) axis, wherein the D axis defines a first path of maximum magnetic resistance of the rotor and the Q axis defines a second path of maximum torque generation. The apparatus further includes a plurality of stator windings for the electric motor, wherein three pairs of stator windings are selected from the plurality of stator windings. The apparatus further includes a controller configured to: determine a delta voltage for each pair of stator windings by sequentially energizing and de-energizing each pair of stator windings, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair; determine a minimum delta voltage based on a minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with a remaining stator winding not included in the corresponding pair; and compare two delta voltages not associated with the minimum delta voltage to determine the proximity of the remaining stator windings to one of the D axis of the rotor and the Q axis of the rotor.

[0087] Alternative embodiments of the apparatus include one of the following features or any combination of the following features. The electric motor comprises a permanent magnet synchronous motor (PMSM). The electric motor comprises a brushless direct current (BLDC) motor. The controller is further configured to sequentially energize and de-energize a pair of stator windings including the remaining stator winding associated with the minimum delta voltage to measure a first rotor delta voltage and a second rotor delta voltage, wherein the first rotor delta voltage is measured by applying a first voltage pulse in an opposite direction to a second voltage pulse used to measure the second rotor delta voltage; and a rotor polarity of the rotor is determined by comparing the first rotor delta voltage to the second rotor delta voltage. The controller is further configured to energize each pair of stator windings by sequentially connecting each pair of stator windings to one of a power supply and ground via corresponding shorting diode connections.

[0088] In another embodiment, a method for initial position detection of an electric motor includes determining a delta voltage for each of three pairs of stator windings by sequentially energizing and de-energizing each pair, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair. A minimum delta voltage is determined based on the minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with a remaining stator winding not included in the corresponding pair. Two delta voltages not associated with the minimum delta voltage are compared to determine the proximity of the remaining stator winding to one of a direct (D) axis of a rotor of the electric motor and a quadrature (Q) axis of the rotor, wherein the D axis defines a first path of maximum reluctance of the rotor and the Q axis defines a second path of maximum torque generation.

[0089] An alternative embodiment of a method for detecting an initial position of an electric motor includes one or any combination of the following features: A pair of stator windings, including the remaining stator winding associated with the minimum delta voltage, are sequentially energized and de-energized to measure a first rotor delta voltage and a second rotor delta voltage, wherein the first rotor delta voltage is measured by applying a first voltage pulse in a direction opposite to a second voltage pulse used to measure the second rotor delta voltage, and the rotor polarity of the rotor is determined by comparing the first rotor delta voltage with the second rotor delta voltage, thereby measuring the first rotor delta voltage and the second rotor delta voltage, wherein the first rotor delta voltage is measured by applying a first voltage pulse in a direction opposite to the second voltage pulse used to measure the second rotor delta voltage, and the rotor polarity of the rotor is determined by comparing the first rotor delta voltage with the second rotor delta voltage. The first and second voltage pulses used to determine the rotor polarity have a long duration capable of magnetically saturating the remaining stator winding associated with the minimum delta voltage. The first and second voltage pulses used to determine the rotor polarity have a short duration capable of preventing the rotor from physically rotating. Energizing each of the three pairs of stator windings includes connecting the respective pairs to one of a power source and ground through respective shorting diode connections.

[0090] Although the present invention has been described herein with reference to specific embodiments, various modifications and changes may be made without departing from the scope of the invention as set forth in the appended claims. The specification and drawings are therefore to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. It is not intended that any advantages, benefits, or solutions to problems described herein with respect to specific embodiments be construed as key, required, or essential features or elements of any or all of the claims.

[0091] Unless otherwise stated, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Therefore, these terms are not necessarily intended to indicate temporal or other priority of such elements.

Claims

1. A method for detecting the initial position of a motor, characterized in that: include: for each of a respective pair of stator windings selected from two of the three stator windings, wherein each of the three stator windings is connected to a neutral node, determining a respective stator delta voltage, each respective stator delta voltage being one of a plurality of delta voltages determined by: applying a first voltage pulse across the respective pair while measuring a respective first voltage at the neutral node, applying a discharge path across the respective pair while measuring a respective second voltage at the neutral node, and determining the delta voltage by subtracting the respective first voltage from the respective second voltage; determining a minimum delta voltage based on a minimum of the absolute values of each of the three respective stator delta voltages, the minimum delta voltage being associated with a remaining stator winding of the three stator windings that is not included in the respective pair; determining a proximity of the remaining stator winding corresponding to the minimum delta voltage to one of a D-axis of a rotor of the electric motor and a Q-axis of the rotor by comparing the stator delta voltages of the two stator windings not associated with the minimum delta voltage; and The rotor polarity of the rotor is determined by comparing a first rotor delta connection voltage with a second rotor delta connection voltage, wherein the first rotor delta connection voltage and the second rotor delta connection voltage are each one of the plurality of delta connection voltages determined based on a pair of stator windings including the remaining stator winding associated with the minimum delta connection voltage.

2. The method according to claim 1, characterized in that The first voltage and the second voltage of the neutral node are measured at ends of the remaining stator windings connected to the neutral node, wherein the remaining stator windings are not energized.

3. The method according to claim 1, characterized in that The first and second voltage pulses used to determine the rotor polarity have a long duration capable of magnetically saturating the remaining stator windings associated with the minimum delta voltage.

4. The method according to claim 1, wherein The first and second voltage pulses used to determine the polarity of the rotor have a short duration capable of preventing the rotor from physically rotating.

5. The method according to claim 1, wherein The minimum absolute voltage corresponds to the U phase, and the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the V phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the V phase is less than or equal to the corresponding stator voltage of the W phase.

6. The method according to claim 5, characterized in that The initial position of the rotor is: When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 0 degrees relative to a reference angle, When the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 180 degrees relative to the reference angle, When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, it is nominally -90 degrees relative to the reference angle, and When the first absolute value of the first rotor delta voltage is less than or equal to the second absolute value of the second rotor delta voltage and the remaining stator windings are close to the Q-axis, nominally 90 degrees relative to the reference angle.

7. The method according to claim 1, characterized in that The minimum absolute voltage corresponds to the V phase, and the remaining stator winding approaches the D axis when the corresponding stator delta connection voltage of the U phase is greater than the corresponding stator voltage of the W phase, and the remaining stator winding approaches the Q axis when the corresponding stator delta connection voltage of the U phase is less than or equal to the corresponding stator voltage of the W phase.

8. The method according to claim 7, characterized in that The initial position of the rotor is: When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D axis, nominally 30 degrees relative to a reference angle, When the first absolute value of the first rotor delta connection voltage is less than or equal to the second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the D-axis, nominally -150 degrees relative to the reference angle, When a first absolute value of the first rotor delta connection voltage is greater than a second absolute value of the second rotor delta connection voltage and the remaining stator winding is close to the Q axis, nominally 120 degrees relative to the reference angle, and When the first absolute value of the first rotor delta voltage is less than or equal to the second absolute value of the second rotor delta voltage and the remaining stator windings are close to the Q-axis, nominally -60 degrees relative to the reference angle.

9. A device for detecting the initial position of a motor, characterized in that: include: a rotor of an electric motor, the rotor comprising a direct axis D-axis and a quadrature axis Q-axis, wherein the D-axis defines a first path of maximum magnetic resistance of the rotor and the Q-axis defines a second path of maximum torque generation; and a plurality of stator windings of the electric motor, wherein three pairs of stator windings are selected from the plurality of stator windings; and A controller configured to: Determining a delta voltage for each pair of stator windings by sequentially energizing and de-energizing each pair of stator windings, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair, comprising: measuring a first voltage and a second voltage at an end of the unenergized stator winding connected to the center tap of each corresponding pair, and determining the delta voltage by subtracting the first voltage from the second voltage; the first voltage being measured by applying a first voltage pulse across each corresponding pair, and the second voltage being measured by applying a discharge path across each corresponding pair; determining a minimum delta voltage based on a minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with the remaining stator winding not included in the corresponding pair, and Two delta voltages not associated with the minimum delta voltage are compared to determine a proximity of the remaining stator winding to one of the D-axis of the rotor and the Q-axis of the rotor.

10. A method for detecting the initial position of a motor, characterized in that: include: Determining a delta voltage for each of three pairs of stator windings by sequentially energizing and de-energizing each pair, wherein the delta voltage is measured through an unenergized stator winding connected to a center tap of each corresponding pair; comprising: measuring a first voltage and a second voltage at the center tap of the unenergized stator winding connected to the center tap of each corresponding pair at an end of the unenergized stator winding, and determining the delta voltage by subtracting the first voltage from the second voltage; the first voltage being measured by applying a first voltage pulse across each corresponding pair, and the second voltage being measured by applying a discharge path across each corresponding pair; determining a minimum delta voltage based on a minimum of the absolute values of each of the three delta voltages, wherein the minimum delta voltage is associated with a remaining stator winding not included in the corresponding pair; and Two delta-connected voltages not associated with the minimum delta-connected voltage are compared to determine the proximity of the remaining stator winding to one of a direct axis (D) of the rotor of the electric motor and a quadrature axis (Q) of the rotor, wherein the D-axis defines a first path of maximum reluctance of the rotor and the Q-axis defines a second path of maximum torque production.

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